test: each app keeps its tests in a tests package

131 test modules sat next to the code they test; instances alone had
51 of them beside views.py and utils.py. They move into a
tests/ package per app, and the JavaScript checks into
webvirtcloud/tests/js. Each non-empty tests.py becomes tests/test_views.py;
the empty generated stubs are removed.

Imports of the app's own modules become absolute, paths built from
__file__ go one level up, the live helper is instances.tests.livetest,
and coverage omits */tests/*. The suite discovers the same 960 tests as
before.

admin/test_user_update_next.py

@@ -1,26 +0,0 @@
-"""After saving a user, the edit page goes back to ?next= only on this site."""
-
-from django.contrib.auth.models import User
-from django.test import TestCase
-from django.urls import reverse
-
-LIMITS = {"max_instances": 1, "max_cpus": 1, "max_memory": 1024, "max_disk_size": 4}
-
-
-class UserUpdateNextTests(TestCase):
-    def setUp(self):
-        self.client.force_login(User.objects.create_superuser("un-admin", "un@example.com", "pw"))
-        self.user = User.objects.create_user("un-user", password="pw")
-
-    def save(self, next_url):
-        url = reverse("admin:user_update", args=[self.user.id]) + "?next=" + next_url
-        return self.client.post(url, {"username": "un-user", "is_active": "on", **LIMITS})
-
-    def test_a_page_of_this_site(self):
-        account = reverse("accounts:account", args=[self.user.id])
-        self.assertRedirects(self.save(account), account, fetch_redirect_response=False)
-
-    def test_another_site_is_not_followed(self):
-        for next_url in ("https://evil.example/", "//evil.example/", "/\\evil.example/"):
-            with self.subTest(next_url=next_url):
-                self.assertRedirects(self.save(next_url), reverse("admin:user_list"), fetch_redirect_response=False)